In order to sell a variety of custom paint colors, paint vendors typically employ a system of mixing paint in custom colors whereby cans of base paint are tinted with various quantities of differently colored pigments in predetermined ratios, according to a process that is well known to those skilled in the art to which this invention relates. Because this tinting occurs in the retail store as the final step before the paint is delivered to the purchaser, it is necessary, for purposes of ensuring that the paint has been properly tinted and that the pigment is thoroughly mixed into the base paint, to blend the paint by one of a variety of methods.
Among the more popular of methods for blending the paint is by agitating the closed container, just after tinting, for some amount of time sufficient to ensure proper blending. While it is possible to blend the paint by manually shaking the container, it is more efficient, quicker, and less tiring to employ a mechanical paint can agitator, which works by moving the container through an iterative series of motions. These mechanical agitators typically fall into one of four varieties: the vibrational, or “case shaker,” variety; the gyroscopic, or “end-over-end” variety; the reciprocal motion variety; and the semi-gyroscopic or “orbital” variety. In the vibrational and gyroscopic agitators, holding the can securely is of particular importance. In the gyroscopic method, the motion of the paint can is typically end-over-end, such that the paint contained therein is blended by virtue of vortices that develop as the paint is acted upon by gravity and the motion of the gyroscope. In the vibrational method, the paint can is rapidly driven in an up-and-down motion, and the paint is blended by vortices that develop primarily because of the inertia of the paint as the can is drawn through the range of motion. The vibrational method typically employs, for mechanical and fluid-mechanical reasons, an elliptical path for the paint can, though which the orientation of the paint can is maintained.
In vibrational and gyroscopic mixers, it is essential that the paint can be firmly gripped, because the can is usually moved through as many as 700 revolutions per minute. The unintended consequences of an undergripped paint can generally include the spillage of paint inside the agitator, which is at best untidy and at worst damaging to the machine (as well as wasteful of paint), and physical damage to the machine or injury to those in proximity, if the can is “thrown” with sufficient force.
In order to grip a can in a vibrational paint shaker, conventional designs have typically utilized a pair of clamping plates. A paint can is placed on the bottom plate, and the top plate is driven downward into engagement with the can; as specified amount of force is applied thereon, and the can is consequently clamped for agitation. Various means for driving the top plate downward have been proposed, and a typical apparatus utilizes a plate mounted, by threaded nuts, on two or more set screws. A motor drives the screws so as to drive the plate up or down, into or out of engagement with the can.
Conventional designs further control the motion of the drive plate by applying an electrical current at a specified, controlled voltage to the motor, and by monitoring the current draw of the motor and the positioning of the screws, can determine by inference if a can has been clamped. Specifically, in conventional systems it has been determined that at a particular level of current draw (which is indicative of the mechanical resistance encountered by the motor in driving the plan downward), it is likely that a can has been encountered, and the plate should be driven to a predetermined amount of pressure (sufficient to hold the can in place during agitation) and held in place.
In such a system, a number of attendant problems are presented. For instance, because of changes in the profile of the screws or the threaded nuts over a period of use, or because of the presence of dried paint, corrosion, dirt, or other foreign matter within the threads, it is possible for a current draw in excess of the predetermined level for indicating the presence of a can to be detected, even if no can is present. If such an operating condition is not detected before agitation begins, serious damage to the machine and waste of paint will almost certainly occur.
Further, because of the rapid nature of the agitation and because of the inertia of the paint can and the paint within the can, it is possible for a gap to develop between either of the clamping plates and the paint can, which can cause unwanted noise, damage to the can or to the machine, and waste of paint. Conventional systems attempt to address this problem by continuing to apply pressure to the can during agitation (which can lead to crushing of the can) or by stopping the agitation cycle (which is inefficient), if a gap develops.
Moreover, because the motors used in conventional systems are typically large and must overcome a great deal of inertia in order to begin agitating the can, a dedicated, specially wired power source is usually employed, which leads to added expense to the store in which a conventional system is used.
Consequently, what is needed is a clamping system that is “smart” in operation—i.e., a system in which the processes associated with sensing the presence of cans are managed more carefully than in conventional systems, such that the system can differentiate between the presence of a paint can and wear or the presence of foreign matter on the threads, and such that it can differentiate between different can sizes and apply clamping pressure accordingly. Also, because different levels of clamping pressure are required in order to hold the load securely, depending upon the size and number of cans present, it is desirable to have a clamping system that can identify the amount of clamping pressure needed to hold the load securely. A further need is felt for a paint can agitator that can be used with a standard, non-dedicated power source.